How might a predictive theory for \(\)  be constructed? [1]} offer an intriguing perspective relating to the frequency of deep convection in the ascending branch. They argue that only when convection is sufficiently deep will there be upper-tropospheric meridional outflow that travels nearly inviscidly (/ with \({\approx 1}\) ) toward either pole; at times and longitudes where deep convection is absent, they argue \({\approx 0}\) . Under those conditions, the time-mean, zonal-mean \(\)  field becomes a function of the spatial and temporal occurrence of deep convection in the ascending branch. This contrasts with the conventional, extratropically focused approach to \(\) , wherein it is controlled by stresses from subtropical and mid-latitude eddies propagating into the deep tropics and breaking [2]}, [3]}.
